Valve assemblies are well known for their ability to regulate fluid flow through inlet and/or exhaust openings. One such valve is a poppet valve. Poppet valves are typically made from heat-resistant steel and include a circular head or valve. The valve includes a conical face which registers with a corresponding valve seat bounding the opening. In some cases the head may be disk shaped and seat over a port opening. In other cases, such as with a ball-poppet valve, the head may be a spherical member which closes the valve when positioned against an opening having a conical or tapering surface. A guided stem, by which the valve is lifted from its seated position, is movable under the urging of an actuator. When the conical face of the valve rests on the valve seat the fluid is sealed from flowing through the valve.
As the materials which form the poppet valve assembly are substantially incompressible, early failure of the valve assembly can result when the valve is employed to dispense fluids containing high concentrations of substantially incompressible and abrasive inorganic additives or fillers. Some fillers, such as Al.sub.2 O.sub.3, can cause frictional wear of the valve when flowing between the valve and the seat. Hertz-type stresses of the mating surfaces, which can cause flaking or shearing at the surfaces, are also known to occur when these solid fillers are pinched between a ball-poppet and the valve seat as the ball-poppet seals against the seat. As the ball-poppet reaches the final closed position there can be relative movement between a particle of the solid filler and the mating surfaces which can gouge the surface, creating a pathway between the mating surfaces through which the fluid may leak.
Furthermore, these solid fillers can become trapped between the mating surfaces as the poppet closes against the seat. Because the mating surfaces and the abrasive filler are all made from substantially incompressible materials, a particle of the filler becoming trapped between the mating surfaces can cause localized stress concentrations on the mating surfaces. Such localized stress concentrations can result in surface imperfections, distortions, and other irregularities, such as pitting or abrasive wear, which prevent sealing engagement between the valve and the seat, and thereby cause valve failure as the fluid will then have a pathway between the mating surfaces.
Some fillers may be crushed between the mating surfaces which can result in degradation of the material being dispensed. Some adhesives include fillers to provide a desired thermal or electrical characteristic to the adhesive. For example, glass spheres are within some dielectric adhesives to provide the desired insulative characteristics. These glass spheres can be about 1/5000 of an inch in diameter. These glass spheres could be crushed if trapped between two incompressible mating surfaces, which could then cause electrical shorts through the material and result in quality control problems for the user.
Currently, valves employed to dispense abrasive fluids employ poppet valves which seat a metal valve against a metal seat. Valve failure has been witnessed in these valves after 50,000 to 60,000 cycles of opening and closing. It would therefore be desirable to provide a valve assembly which provides suitable sealing characteristics between the valve and the valve seat and which minimizes the risk of failure when dispensing abrasive products.